Pb poising is a public health concern in many developing countries, as well as in some industrialized and developed countries (2). There is no known safe level of exposure, particularly in children. Most studies that have been published on population Pb exposure used the old cutoff of Pb safety level of ≥ 10 µg/dL. Therefore, there is a great need to reassess the population Pb exposure, particularly in areas where the average exposure level was ≥ 5 µg/dL. Several studies have been published from many countries since the revision of the safety limit of Pb exposure in children, but these studies are mostly based on populations living in high exposure environments and in those who are occupationally exposed to Pb. Kuwait, being a petrochemical industry-based economy with heavy traffic burden along with its associated industry (automobile repair workshops, etc.), is expected to have high level of Pb exposure (9). In addition, the excessive use of ammunition and the burning of oil wells during the 1991 Gulf war might also have its impact on the environmental Pb levels. However, studies on the population Pb exposure, using representative samples are non-existing. Studying Pb exposure in children and adolescents is particularly important due to the well-known and long-lasting adverse effects of low-level Pb exposure on brain development and function. Approximately, 25% of the population in Kuwait is under the age of 19 years. This study is based on a nationally representative sample of adolescent school children.
The median blood Pb was 5.1 µg/dL. However, a significant proportion of subjects (51%) had Pb levels above the CDC/WHO cutoff of ≥ 5 µg/dL, and this proportion was even higher (56%) in female subjects. About 13% of the subjects had Pb levels ≥ 10 µg/dL. Similar results have been reported in children and adolescents (age range 4–19 years) from Saudi Arabia, with mean Pb of 4.94 µg/dL and 50% with blood Pb level ≥ 5 µg/dL (21), and Indonesia, with 47% having Pb level ≥ 5 µg/dL (22). A study from Egypt reported mean Pb levels similar to ours (5.6 µg/dL) but in this study 57% of study sample had Pb levels ≥ 10 µg/dL (23). The prevalence of Pb exposure in our study was lower than many developing countries such as Senegal [61.7% >10 µg/dL] (24), Bangladesh [87.4% >10 µg/dL] (25), Nepal [84% >10 µg/dL] (26), India [47% >10 µg/dL] (27), Mexico [64% >5 µg/dL] (28) and South African countries [80–98% >10 µg/dL] (29). On the other hand, the average Pb levels from many developed countries were lower than the median Pb levels in this study. Examples are average blood Pb levels from the Unite States [1.9 µg/dL; 3.8% >5 µg/dL] (30), Sweden [1.4 µg/dL], Poland [1.63 µg/dL], Czech [1.55 µg/dL], Slovakia [1.9 µg/dL] (31), France [1.49 µg/dL] (32) and Canada [0.48 µg/dL] (33). Variations in sampling (whether from general population or high exposure environment), age and the degree of implementing legal restriction to minimize or restrict the use of Pb are possible reasons for these variations in the prevalence of Pb exposure (34, 35).
Striking differences were observed in the Pb exposure among the six Governorates, both in the median blood Pb levels and in proportions of subjects with Pb levels above the cutoff value. The differences among the Governorates remained significant after adjusting for several confounding variables that are known to be associated with Pb levels in the literature such as sex, age, smoking and anemia status. In terms of the median blood Pb levels, the entire distribution of males in Al-Asima and females in Mubarak Al-Kabeer and Al-Ahmadi were above the cutoff value (Fig. 1B). The Governorates of Al-Asima, Al-Ahmadi (both male and female schools), Al-Jahra (male school) and Mubarak Al-Kabeer (female school) stood out as the areas with the high proportions of subjects with high Pb levels, particularly above the cutoff of ≥ 10 µg/dL (Table 3). Two previous studies (36, 37) from Kuwait also have reported significant differences between the residents from residential and industrial areas.
Several factors could be responsible for the high exposure of Pb in these areas. For example, the schools that were selected from the Al-Asima Governorate, both male and female, are close to each other and are in close proximity to three major highways and one coastal road with a very heavy traffic burden. This is the oldest location in Kuwait, where most Kuwaiti people lived before the discovery of oil. It has old buildings, hundreds of automobile repair workshops, the main commercial port in the country and an industrial area. Another Governorate with high Pb exposure in both male and female subjects is Al-Ahmadi. Most oil fields, oil refinery and petrochemical industries are located in this Governorate. Soil and air sample from this Governorate have been reported to contain higher levels of Pb compared to other Governorates (10, 12). In addition, this Governorate has an agricultural site (Al-Wafra), where vegetables, fruits and dates are cultivated. The use of pesticides and fertilizers in these forms might also have contributed to the soil and air Pb content. Soil Pb content in samples from Al-Wafra was reported to be higher than the normal acceptable limits (38).
The high blood Pb levels in the governorates of Al-Asima and Al-Ahmadi is supported by a study on the indoor air quality in different schools; three from urban residential area and four from industrial area (39). Pb content in the dust particles (PM10) collected from air conditioner’s (AC) filters in the classrooms was the highest (74.30 µg/g) in one school from the industrial zone (Bnediar boy’s school). This school is located in Al-Ahmadi governorate near Mina Abdullah refinery. Pb content in PM10 dust particles form the three schools from residential area were also high (ranging from 40.3 to 50.0 µg/g), compared to the remaining three schools from industrial zone which were away from the oil refinery (ranging from 19.1 to 23.3 µg/g). The three schools from residential areas were from the Al-Asima governorate, and one of these schools is included in this present study. These data match with the BPbLs in schools from these Governorates and suggest that environmental air pollution from oil installations and industrial activity is the main source of Pb exposure in school children.
The Governorate of Mubarak Al-Kabeer is located next to the Al-Ahmadi Governorate and the spill-over of the environmental Pb contamination is suspected to be the reason for high blood Pb levels. In addition, this is a newly developed area with a lot of construction activity. The exhaust from the construction machinery, together with the rising dust from the soil might also contribute to the Pb exposure. The particularly high Pb exposure in the female school from this Governorate is of significant public health concern, as there might be a local source of contamination. It has been reported that in 2018, the Public Authority for the Environment, Kuwait asked the Ministry of Education to close drinking water supply in 13 different schools, as the water was not suitable for drinking (Al-Anba News Paper dated March 2, 2018). The reason mentioned for the closure of drinking water supply in these schools was the lack of maintenance of filters, internal water supply networks, reservoirs and chillers for drinking water. It is of interest to note that six out these thirteen schools were from Mubarak Al-Kabeer Governorate, although the school which was selected in this study was not specifically mentioned.
Flaring of the unwanted gases from the extracted crude oil is a common practice in oil extraction and refining and is considered a major source of emission and air pollution in oil producing countries like Kuwait (40). Heavy metals including Cd, Hg and Pb are found in crude oil and gas and are emitted to the environment from flaring (41). Middle East have the highest flaring rate with 80.99 metric ton (MT) in the year 2018 (42). The estimated emission of Pb from flaring is estimated to be 4.3 mg Pb/ton throughput from the associated gases and 5.4 mg/ton throughput from the non-associated gases (43). Thus, in Kuwait, emission of Pb into the environment from gas flaring is a potential source of environmental Pb exposure. This may be particularly relevant in the Ahmadi and Mubarak Al-Kabeer governorates, which are close to oil installations. The Kuwait National Petroleum Company (KNPC) has adopted several measures to curb emissions and to protect the nearby communities (44). It has recently (in 2018) installed a fully functional flare gas recovery unit to curb emissions. However, the Pb emitted from gas flaring in the past may still exist in the environment (air and soil), which may still be a source of environmental exposure.
In the Al-Jahra Governorate, the proportion of subjects with Pb ≥ 10 µg/dL was 12% in male subjects, compared with 2.5% in female subjects. The male school selected form this Governorate has several features that might have contributed to the high exposure of Pb. For example, this school is close to the major highway and is located in the middle of two major industrial zones (Jahra and Sulaibiya). It is in close proximity to a waste-water treatment plant, a cable and electrical appliances factory and an oil and pipe manufacturing unit. The female school is 16 Km away from this site. Lead-acid batteries are one of the major industrial sources of Pb accumulation and exposure. In Kuwait, there is one lead-acid battery recycling unit, which is located in Al-Jahra governorate, closer to the boy’s school. Although, the Kuwait EPA has several regulations (Law Number 42; Decision No. 8, for example) to monitor and restrict the emission of toxic wastes, it is not clear to what degree these restrictions are implemented. Moreover, dust and Pb particles can be transferred to a wider community by workers, if they are not taking correct precautions and safety steps (45). In developing countries, unregulated lead-acid batteries recycling practices are a major source of Pb toxicity and environmental accumulation (22, 34). In the USA lead-acid batteries’ manufacturing and recycling factories are still considered a source of contamination of the soil, air and water despite all the regulations and monitoring by the EPA (45). The Governorates of Hawally and Farwaniya are mostly residential and, although very congested with heavy traffic burden, have lower level of Pb exposure. This suggest that the source of Pb exposure in Kuwait is mostly from oil installations and industrial activity.
The median blood Pb was significantly higher in female subjects compared to male subjects, however, this relationship was not the same across all the Governorates. Significant sex-Governorate interaction was noted; in some Governorates, males had significantly higher Pb level than females and the opposite was true in others, and no difference in still others. Similar pattern was also observed in the proportion of subjects above the cutoff points, either at ≥ 5 µg/dL or at ≥ 10 µg/dL. In, Female sex was significantly associated with Pb ≥ 5 µg/dL in the univariate logistic regression, but this association did not remain significant in the multivariable analyses. This suggest that other factors might have confounded this relationship. Similar to ours, some studies also reported the lack of association with sex (23, 30); while others have reported significant differences between males and females in the same age group (21, 31, 46). Higher levels of Pb in female subjects in some Governorates could be due to certain differences in daily practices between boys and girls in Kuwait. Girls use Kohl and other cosmetics that may be contaminated with Pb (47). Anemia, which is associated with high Pb levels in some studies, is usually higher in females (48, 49). However, anemia in this population in female is considered moderate (11%), which can explain the lack of association between female sex and high Pb level in Kuwait.
To our knowledge, this is the first properly designed study utilizing a nationally representative sample of adolescents from Kuwait. We employed a very sensitive method of Pb estimation (ICP-MS) with strict quality control measures. Our method recovered 96.8% (S1) and 96% (S2) of Pb in the samples with known of Pb content (Seronorm). There are, however, a few limitations in this study. First, dietary history and food intake was not evaluated as a possible factor of Pb exposure. Second, father or mother occupational details were also not taken into account which could provide a clue to the exposure source. Third, subjects were selected from schools and Pb data from other members of the household was not available. As such it is difficult to discern whether the source of Pb is from household or from the school.